This invention relates to switched capacitor circuits and more particularly either to one for generating a single-sideband signal or to one that is capable of performing amplitude modulation and/or demodulation functions.
Advances in MOS-LSI technologies and the development of switched capacitor techniques have improved the possibility of analog signal processing being done on a single chip. In order to perform such analog signal processing in a fully integrated circuit, however, circuits performing modulation and demodulation functions must be included. In the past, modulators and demodulators have historically employed resistors. It is desirable to achieve these functions in integrated circuits without using resistors, however, since integrated resistors require a considerable surface area of the associated semiconductor chip. A switched capacitor demodulator which does not require resistors is disclosed in the article Switched-Capacitor Building Blocks for Adaptive Systems by K. Martin and A. S. Sedra, IEEE Transactions on Circuits and Systems, Vol. CAS-28, No. 6, June 1981, pp. 576-584. Martin's demodulator comprises a switched capacitor low-pass filter with a switched input signal, see Section VI, pp. 580-581, and FIGS. 11 and 12 there. Switched capacitor modulators and/or demodulators are also briefly described in the article Switched Capacitor Quadrature N-Path Filters by M. Zomorrodi, Midwest Symposium on Circuits and Systems, pages 682-686, June 1981. Structure for generating single-sideband signals is illustrated and described in Principles of Communication Systems by H. Taub & D. L. Schilling, pp. 102-104, McGraw Hill Book Co., Copyright 1971.
An object of this invention is the provision of resistorless circuitry for use in performing amplitude modulation and/or demodulation functions.